The present invention generally relates to magneto-optic disk units, and more particularly to a magneto-optic disk unit which plays a cartridge type magneto-optic disk.
Presently, a magneto-optic disk unit which is designed to play a cartridge type magneto-optic disk is being developed. Such a cartridge type magneto-optic disk is made up of a cartridge which accommodates a magneto-optic disk, similar to a cartridge type magnetic disk which is played on a magnetic disk unit. For example, when a magneto-optic disk with a 3.5-inch diameter is accommodated in a cartridge with a shutter, the external appearance of the cartridge becomes similar to that of the existing 3.5-inch magnetic disk cartridge.
Because the magneto-optic disk has a thickness greater than that of the magnetic disk, the magneto-optic disk cartridge is thicker than the magnetic disk cartridge. For this reason, a cartridge holder of the magneto-optic disk unit is bulky compared to a cartridge holder of the magnetic disk unit. Therefore, the magnetic disk cartridge may be erroneously inserted into the magneto-optic disk unit.
FIGS. 1A and 1B are diagrams for explaining the problems of the prior art. In FIGS. 1A and 1B, a magnetic disk 1 is accommodated within a magnetic disk cartridge 2. A magneto-optic disk 3 is accommodated within a magneto-optic disk cartridge 4. A magneto-optic disk unit 5 has a cartridge holder 6, and a magnetic disk unit 7 has a cartridge holder 8.
As shown in FIG. 1B, it is possible to insert the magnetic disk cartridge 2 into the cartridge holder 8 of the magnetic disk unit 7 as indicated by an arrow 9. But, because the magneto-optic disk cartridge 4 is thicker than the magnetic disk cartridge 2, the magneto-optic disk cartridge 4 cannot be inserted into the cartridge holder 8 of the magnetic disk unit 7 as indicated by a crossed out arrow 10.
However, as shown in FIG. 1A, both the magneto-optic disk cartridge 4 and the magnetic disk cartridge 2 can be inserted into the cartridge holder 6 of the magneto-optic disk unit 5 as indicated by arrows 11 and 12, because the thickness of the magnetic disk cartridge 2 is smaller than that of the magneto-optic disk cartridge 4.
A permanent magnet (not shown) for applying an external magnetic field is provided within the magneto-optic disk unit 5. For this reason, when the magnetic disk cartridge 2 is erroneously inserted into the cartridge holder 6 of the magneto-optic disk unit 5, the data pre-recorded on the magnetic disk 1 may be damaged or erased by the permanent magnet.
Therefore, it is necessary that the magneto-optic disk unit 5 prevent an erroneous insertion of the magnetic disk cartridge 2. However, there is a problem in that the conventional magneto-optic disk unit 5 has no means for preventing such an erroneous insertion.